To fully understand the formation of neuronal circuitry in the developing brain, we must study synaptogenesis at a molecular level. The proposed work will investigate alterations in molecular and structural properties of the morphological synapse during brain maturation. In previous studies we have identified and characterized carbohydrates, lipids, proteins, glycoproteins and enzymes that are present in mature synaptic junctions. Some of these synaptic molecules included tubulin and actin, a distinct postsynaptic density polypeptide, a class of external postsynaptic membrane glycoproteins that bind Con A, a Ca ion modulated Mg ions -Atpase and cyclic AMP-dependent protein kinases. This information, in part, represents a strong foundation on which our studies of the developing synapse can be based. First, we will systematically optimize conditions for isolating highly purified and morphologically intact synaptic junctions from immature cerebral cortex. In preliminary studies, we have successfully isolated synaptic junctions at different times during the course of in vivo synaptogenesis. Second, we will examine age-dependent changes in proteins and glycoproteins of isolated synaptic junctions. Using membrane surface labeling we will examine the appearance and topographical orientation of developmentally regulated synaptic membrane surface components. Special attention will be paid to determine differences in the molecular composition between extrajunctional and synaptic junctional plasma membranes. Covalent cross-linking studies will be used to investigate protein-protein interactions that are related to changes in the molecular organization of synaptic junctions during development. Cyto- and immunohistochemical methods will be used to examine the distribution of the filamentous proteins tubulin and actin and cell surface glycoproteins that bind Con A. Furthermore, we will determine if these components constitute a postsynaptic "surface modulating assembly" (a complex that has been theorized to function in the segregation and stabilization of important molecules at the site of synapse formation). The results of these studies will provide a multidisciplinary approach to investigating relationships between molecular composition and organization and the morphology of synapses assembled during development.